1. Field of Invention
The present invention relates to syringes which can accurately meter small volumes of fluid. In one embodiment, the syringe has dual resolution capability which enables the aspiration of a tiny sample and also the dilution of the tiny sample with a much larger-volume of reagent (or another sample) with the same syringe.
2. Discussion of Related Art
In recent years, diagnostic and analytic tests have required smaller and smaller samples to be accurately metered, both to mix or dilute the samples with larger volumes of various reagents (sometimes in high dilution proportions) and to transfer them separately. There is a demand for samples less than 1 microliter and even less than 100 nanoliters or even 10 nanoliters to be aspirated arid delivered using a syringe or pipette system. Unfortunately, positive displacement devices that can accurately pick up the minute volume of the sample cannot provide enough flow to completely transfer the sample and cannot also meter large reagent volumes. Often times when transferring the sample, the sample will hang onto the tip of the syringe, which requires touching the sample to another surface to free it from the capillary action and surface tension. A touchless transfer, where the sample is ejected out of the syringe with enough force to prevent the sample from hanging on the tip of the syringe, is desired. One way to increase the ejection force of a syringe is to use a syringe with a larger diameter. Yet when the diameter of a syringe is increased to be able to impart the flow rate needed to prevent the xe2x80x9changing dropxe2x80x9d occurrence, the accuracy of the size of the sample aspirated is compromised. While a larger diameter syringe can effect a touchless transfer, it cannot precisely aspirate a tiny sample, such as one as minute as 10 nanoliters.
Multiple pistons of different diameters contained within a single pipette chamber or cylinder such as described below have been known in the past. In such pipettes, spring means are used to keep the pistons in an upper position with a thumb-pressed button so that the pistons can be moved against the force of helical springs to a pre-determined lower position. These systems have been used for a variety of purposes, including the transfer of small volumes of fluids.
In U.S. Pat. No. 5,383,372, assigned to DRD Diluter Corporation, a design is provided with a plurality of pistons that move together and separately in a pipette chamber to measure a small sample and then dispense it with an air blowout to completely remove the sample. While these systems have provided the capability of dispensing small samples with some significant air blow-off or touchless transfer, the demand for using smaller and smaller samples require systems and devices which permit the aspiration and ejection of smaller and smaller samples. These requirements become more acute with the development of programs for genetic testing of patient""s blood and blood derivatives. Minute aspirations of less than 100 nanoliters and often even 10 nanoliters are now becoming important.
In many instances, it is desirable to deliver the samples by a xe2x80x9ctouchlessxe2x80x9d system that does not require the samples to be touched by another surface, washed out by another liquid, or delivered beneath the surface of another liquid. Therefore new delivery and syringe means are required. Satisfying these developing requirements has been difficult because drops tend to hang onto the tip of the delivery tube forming a hanging drop. The size of the hanging drops can vary widely, and syringes or single piston devices with resolution fine enough to pick up tiny samples simply do not have the flow power to cleanly blow off the sample. A typical sample must be given a velocity when leaving the tip of the probe or pipette of at least approximately 1 meter per second to break free. The smaller the sample, the greater the inaccuracy caused by a hanging drop remaining on the syringe tip. For a variety of reasons, this escape velocity is particularly difficult to achieve with the very small syringes needed to handle very small samples. The problem is further complicated by the requirement that these transfer devices or pipettes be useful for materials that have a widely varied viscosity, from blood derivatives like serum to chemicals like DMSO to various viscous genetic brews. The viscosity variation introduces further variations in the ability of a given sample to escape a confining tip.
Past efforts to achieve desired results involve the miniaturization of syringes to meter smaller and smaller samples. However, small syringes lack the flow power necessary to expel tiny samples. Smaller and smaller probe and pipette tips were developed so that the lower flow rates and pressures the small syringes were able to deliver were artificially increased in an effort to achieve a tip escape velocity. Tips with internal diameters as small as 0.010 inches were developed and in recent years solenoid valve approaches have relied on sapphire drill channels as small as 0.002 inches to provide a sufficient velocity lift at the tip. These delivery tubes result in very long narrow columns of liquid passing through the syringe orifice, which exposes a significantly large proportion of the total fluid volume to damaging surfaces. As a result, genetically related assays which helped trigger the interest in smaller pipettes are compromised because the samples are damaged by the extensive surface area contact to which the assay material is subjected. Therefore, to prevent extensive surface area contact damage to the sample, it is beneficial to not use an excessively small probe tip.
The demand for means and methods for metering very small volumes of material with significant resolution is increasing the need for pumps and pipettes having resolution as fine as that provided by a 10 microliter or even 1 microliter syringe likely required in the future. These precise requirements for accurate metering of very small quantities of material present additional problems. For example, glass is a choice material because much diagnostic work benefits from clear glass for visual inspection. In addition, glass is chemically very inert. However, manufacturing glass tubes with very small internal diameters precise and accurate enough to achieve resolution equivalent to that of a traditional 10 microliter syringe is costly due to the small dimensions. Due to the rugged manufacturable larger sized components of the present invention, prior problems associated with manufacturing tiny syringes are obviated.
Furthermore, traditional syringes for metering small and minute volumes of fluid are troubled with sealing problems. Teflon seals are the industry standard due to its low coefficient of friction and Teflon is chemically inert. However, Teflon has the undesirable characteristic of a high coefficient of thermal expansion and its size can vary considerably with temperature. These slight changes in properties are negligible with a large syringe, but are physically noticeable with traditional syringes that can handle small volumes of fluid. At room temperature, a Teflon seal fit for the internal diameter of a glass syringe can slide smoothly within the housing and seal inside. However at cooler or warmer temperatures, the Teflon seal can be too loose or too tight and xe2x80x9cstickxe2x80x9d therefore the piston cannot be moved as smoothly within the housing or the seal leaks. Since the present invention is able to achieve the resolution of a small syringe with larger components, thermal variations of the sealing material are enormously reduced with the present invention.
Additional concerns not only center on the need to meter smaller and smaller samples with finer resolution, but also there is an increasing need for a more efficient method and means for delivering the selected sample in its entirety without damaging it. As noted, systems used heretofore commonly attempt to solve this problem by adopting probes and tips with artificially small diameters intended to increase the tip velocity of the material being delivered. These efforts have resulted in mechanisms that produce a ratio far in excess of 10:1 between the length of the sample streaming through the tip and the diameter of the sample, which means greater exposure of the material being delivered to surface contact. Applicant has found that if the height to diameter ratio of the sample in a probe or pipette tip is not greater than 10:1 the sample is likely relatively undamaged due to surface area contact. Furthermore, Applicant found that approximately 1:1 to 10:1 may be optimal for blowing or blasting off discrete samples cleanly without damaging them. Applicant has found for a sample as small as 20 nanoliters (0.02 microliters), for example, a probe that is 0.011 to 0.012 inches in internal diameter will support a stable slug of liquid with a healthy height to diameter ratio of 1:1 whereas a solenoid driven sapphire probe ID of 0.003 inches would require a column 80 times as tall as it is across. For samples in the 100 nanolitersxe2x88x921 microliters range, a probe diameter of 0.016 to 0.022 inches will permit a healthy sample height to diameter ratio roughly in the 1:1 to 10:1 range, but blowing off such a sample through such a healthy diameter probe with conventional techniques would require a syringe or plunger or piston much larger than could accurately meter or aspirate the sample to start with.
Traditional single piston syringes used for aspirating minute samples are difficult to prime and keep clear of trapped bubbles. Due to the small volume of the fluid sample, a few tiny air bubbles in the chamber can cause a high percentage of measurement error. Furthermore, the tiny outwardly pressing wiper seals of traditional small syringes wear out quickly. Efforts to get around these seal problems have led to using o-rings and compression seals through which a piston slides, however problems have arisen due to the sizes involved. For example, a traditional single piston 100 microliters syringe has an inside diameter of only 0.057 inches (1.4 mm) and a 10 microliters syringe has an ID of only 0.018 inches (0.46 mm). Therefore, trying to seal such a plunger or piston is essentially like trying to seal a needle. The above mentioned sealing and bubble entrapment problems have led to development of non-positive displacement techniques such as piezoelectric technology and solenoids, but these tend to be expensive or require frequent timing-related calibration or are prone to clogging.
Further, the tiny ID of such small glass syringes are difficult to manufacture. The accuracy of measurement using a syringe is at best only as accurate as the tolerances involved with manufacturing. The present invention succeeds in addressing this problem by grinding or lapping the outer diameters of the piston rather than trying to control the inside diameter of the tubing. When the tubing is glass it is typically formed over mandrels. The best commercial glass tubing production technique for a 1 milliliter syringe cannot control the inside diameter better than +/xe2x88x920.0005 inches, or in extreme special cases down to +/xe2x88x920.0002 inches. However, using precise outer diameter grinding techniques, the present invention can control the OD to more than an order of magnitude greater. The Applicant has found that this precise grinding of the outer diameter of the piston can be done to match the measured ID of lots of glass tubing to produce a differential resolution as fine as a 1-10 microliter conventional syringe. For example, if one needed resolution as fine as a 10 microliters syringe, such as to aspirate 25 nanoliters, the conventional single piston syringe ID would need to be 0.01814 inches. This small size may be impractical for automated use. With the present invention, the same resolution may be accomplished with a glass tube with a practical sized ID of 0.1814 inches and a piston with an OD of 0.1804 inches. Without sacrificing resolution capabilities, the present invention includes practical sizes to work with and to manufacture.
Continuing with the above example, if the inside diameter of a manufactured+lot of glass tubing was actually 0.1811 inches (rather than the intended 0.1814 inches) due to manufacturing variance, if undetected this could result in errors up to 20% in a dual resolution syringe. However, with the present invention, one can compensate for the varied ID of the glass tubing lots by adjusting the grinding amount of the outside diameter of the piston. Grinding the OD of the piston to 0.1802 inches (rather than 0.1804 inches) will easily compensate for inherent variations in the manufacturing process of the glass in the example above. As explained in more detail below, because the present invention may use the difference in the cross-sectional areas between the glass chamber and the piston it not only permits practical minute volume resolution but it can also compensate for the sometimes relatively crude manufacturing tolerances of glass tubes.
The present invention overcomes prior limitations of conventional syringes that cannot accurately meter small volumes of fluid and/or that do not have dual resolution capabilities. Another feature of the dual resolution capabilities provided by the present invention is the ability to facilitate a touchless transfer of a fluid sample from the tip of the syringe. Furthermore, this invention permits positive displacement fluid metering technology to handle small samples along the order of magnitude of microliters (thousands of a milliliter) and even nanoliters (thousands of a microliter). The dual resolution feature also permits the aspiration resolution to differ from the dispensing resolution.
In one illustrative embodiment of the invention, a syringe is provided with dual resolution capabilities. The syringe comprises a housing with a chamber formed therein with a plunger and a piston movable within the housing. The volume of the chamber may vary by movement of the piston or plunger or housing. The chamber may further be defined by a first and a second portion of the chamber wherein the volumes of each portion may change independently of one another.
A method of transferring minute quantities of fluid is also provided, and in another embodiment a method of transferring multiple fluid samples from a single aspirated sample is provided.
In another illustrative embodiment, a syringe is provided operating only under differential capabilities. The invention also includes a device that is capable of diluting a minute sample with an external or internal reagent. Furthermore, the present invention provides a method for metering fluid samples where the aspiration resolution differs from the dispensing resolution.
The present invention helps to overcome the existing problems with the prior art. The dual resolution syringe provides two modes where substantially different volumes of fluid can be metered. Through experimentation, it was found that a large Bulk Mode flow capacity like that of a 1 milliliter syringe in conjunction with a very fine Differential Mode resolution like that of a 10-100 microliters syringe is able to transfer 0.05-1 microliters liquid aliquot and then touchlessly transferring the liquid aliquot by utilizing an interposed air gap. This air gap is designed to be large enough to permit the syringe to dispense the sample out of the syringe while in Bulk Mode. For example, the dual resolution syringe picks up a tiny sample of approximately 1 microliters in the Differential Mode and then uses the Bulk Mode to touchlessly transfer the sample by ejecting the sample out of the syringe along with most of the preceding relatively large 10-15 microliters air gap. Or the dual resolution syringe picks up a minute 0.05 microliters (50 nanoliters) sample and similarly ejects it with most of a preceding relatively huge 2-4 microliters air gap. With the dual resolution syringe, the interposed air gap can be perhaps 1-15 microliters with an aspirated sample volume of 10 nanoliters to 1 microliters. In the present invention, the syringe size utilized in most of the examples provides a difference in the resolution of the two modes of operation of a factor of approximately 100, which was found desirable in experiments.
The present invention also facilitates high ratio dilution by the accurate aspiration of a minute sample combined with the aspiration or internal metering of a relatively large volume of a dilution fluid all by the same device. The volume of the dilution fluid will typically be at least 10 times greater than the volume of the sample. Prior art syringes that could meter the volume required by the size of the dilution fluid are not able to aspirate a minute sample with precision and accuracy. The dual resolution capability of the present invention enables the accurate aspiration and combination of widely different volumes of sample and diluent.
Furthermore, the present invention permits positive displacement fluid handling technology to be used in conjunction with samples in the microliter and nanoliter scale. xe2x80x9cPositive displacementxe2x80x9d simply means that a space-occupying mass or positive displacement element, such as a piston, enters a fluid-filled space and displaces that fluid from the space in a volume equal to that of the positive displacement element that enters the space. Typical positive displacement syringes are limited in measuring smaller and smaller samples due to manufacturing tolerances, seal performance, difficulty in priming with fluid and clearing trapped air, and general size constraints. In one embodiment, the present invention utilizes the Differential Mode to successfully meter samples as small as 10 nanoliters, exemplifying the use of positive displacement fluid handling technology unhampered by previous size limitations associated with conventional syringes, that by their design have no differential capabilities.
Further the present invention is designed to readily be retrofitted into an existing conventional syringe drive system and module. Previous dual resolution designs, such as the previously discussed U.S. Pat. No. 5,383,372 patent, required a completely new system of supporting hardware. The design of the present invention enables it to be configured and sized similar to conventional syringes and may be readily adaptable to and generally used directly in conventional single piston drive systems. This provides one with the ability to easily upgrade a conventional syringe system to a dual resolution syringe. There is a vast array of prior art conventional single piston syringes equipped with a drive system. With the present invention, one can take out the conventional syringe and replace it with the present invention and have a dual resolution syringe system because the present invention is compatible with the existing supporting hardware for conventional syringes. Additionally, the present invention is applicable to both reusable and disposable syringes.